c#之抛出 WebException 的代码在 .NET 3.5 中有效，但在 4.0 中无效

我正在编写代码来检查文件是否存在。如果文件存在，它应该抛出 WebException。代码如下；如果我在 .NET 3.5 中运行此代码，它会抛出 WebException，但如果使用 .NET 4.0，则不会抛出异常。我希望抛出异常，以便我可以验证文件是否存在。

bool IsExists = true; 
try 
{ 
    // string ftpServer = "FTP://111.111.111.111/16FebTo15Mar/Backup/MT_Backup/"; 
    string userName = "gff"; 
    // string filename = "sachin"; 
    string password = "gff@123"; 
    string ftppath= "FTP://111.111.111.111/16FebTo15Mar/Backup/MT_Backup/bh/";  
                    // Ftpurl + new FileInfo(EmpFldr).Name + "/"; 
 
    FtpWebRequest request = (FtpWebRequest)WebRequest.Create(ftppath); 
    request.Credentials = new NetworkCredential(userName, password); 
    request.Method = WebRequestMethods.Ftp.PrintWorkingDirectory; 
    // request.Method = WebRequestMethods.Ftp.MakeDirectory; 
    FtpWebResponse response = (FtpWebResponse)request.GetResponse(); 
} 
catch (WebException ex) 
{ 
    IsExists = false; 
} 
return IsExists; 

请您参考如下方法:

如果你想通过 FTP 检查文件是否存在，那么 check out this answer .

I'd recommend using the following WebRequestMethod instead, this works for me on all servers I tested, even ones which would not return a file size.

WebRequestMethods.Ftp.GetDateTimestamp